I didn't update it. I updated application.xml to version 6 but I get the same errors.

I forgot to mention that before that change (and now) it appears as well this warning: (the same with all JARS in Class-Path)

16:26:07,941 WARN [org.jboss.as.server.deployment] (MSC service thread 1-4) Class Path entry framework.jar in "/C:/dev_software/app_servers/jboss/jboss-as-7.1.1/bin/content/systao.ear/AgendaEJB.jar" does not point to a valid jar for a Class-Path reference.

answer to 2) we just have EJB2.1 so I don't know if need to update to jboss-ejb3.xml file format.

I decided to migrate the application from JBoss 4.2.3 to JBoss 6.1.0 and then do the migration to 7.1.1.

Errors that appear in 6.1 are more understandable than the errors I got in 7.1.1 (basically I have had to change things in configuration files). I almost have the application deployed correctly. Then I will migrate it to 7.1.1 and I will let you know if I success or get more errors.

answer to 2) we just have EJB2.1 so I don't know if need to update to jboss-ejb3.xml file format.

Yes you will have to replace the jboss.xml (if you had one) with the new jboss-ejb3.xml.

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Errors that appear in 6.1 are more understandable than the errors I got in 7.1.1 (basically I have had to change things in configuration files). I almost have the application deployed correctly. Then I will migrate it to 7.1.1 and I will let you know if I success or get more errors.

I would never go that path. You probably will end up doing more work with this approach because the fact that your application configurations need to change for AS7 will not change and some later day you still will have to do those changes when you migrate to AS7.

I haven't fully read this thread (will do in a while), but I believe it should be possible to get your application running fine in AS7 with some relevant changes.